The proposed research will continue our studies of the functional significance and evolutionary origins of the genetic polymorphism in class II (Ia) genes of the major histocompatibility complex (MHC), focusing on rodents. We will extend our characterization of the roles of polymorphic amino acid residues in determining the efficacy of Ia antigens in binding processed foreign antigen and in T-cell recognition of the Ia-Ag complex. Several different sets of antigen-specific T cell clones and hybridomas will be used: I-A-restricted T cells specific for a myelin basic protein peptide, azobenzenearsonate-tyro-sine, or peptides from hen egg lysozyme, and I-E-restricted T cells specific for myoglobin. The latter will be used to explore the functional significance of the absence of polymorphism in the E alpha chain. To characterize the repertoires of T cell receptors specific for a given Ia-Ag complex (in particular, to examine the variety of different registers or views by which the receptors interact with the Ia-Ag complex), we will sequence the receptors of T cells with well-characterized Ia and Ag fine specifities and create hybrid receptors to probe regions involved in Ia or Ag discrimination. The origins and functional significance of heterogeneity in Ia glycosylation will also be explored. The knowledge obtained should facilitate development of immune therapies for treating autoimmune diseases. We will also extend our studies of the evolution of class II polymorphism by studying the class II genes of rodent species belonging to subfamilies of the family Muridae distinct from mice and rats, namely Peromyscus, Microtus, and Spalax. We will characterized the numbers and organization of class II genes, the expression of their RNA and protein, and their sequences, using PCR amplification. These studies should help to characterize the variability in class II gene usage in rodents and to trace the origins of class II polymorphism.